FIG. 2 shows a previously proposed non-prior-art illumination control arrangement for use in a system of the nature shown in FIG. 1. As shown in this latter mentioned figure, a instrument panel A is arranged to house an instrument arrangement B which displays data such as the vehicle speed in two different locations at the same time. Viz., the arrangement includes a speedometer C which is located in a normal position on the instrument panel and a projection arrangement which includes a image generating unit D, and a mirror E which is arranged to reflect the image produced by the image generating unit D onto a windshield F of the vehicle in the illustrated manner. With this system it is possible for an observer (e.g. driver) to ascertain the vehicle speed by observing either the image produced on the windshield or by observing the speedometer in the conventional manner.
The control arrangement basically comprises a microcomputer 1 and first and second display units 2, 3. The microcomputer includes an interface 4 which is supplied with input signals from a light switch 5 and a manually operable up/down illumination control switch 6. The light switch 5 is arranged to be circuited in series between a battery 7 and the interface 4.
The first display unit 2 forms part of the instrument display while the second unit 3 forms part of the HUD system (head-up-display system).
The interface 4 is operatively connected with an illumination control circuit 8 which in this instance includes a memory in which wave shape data is stored, and a wave generating circuit which utilizes the stored data to produce wave shape signals and an up/down counter for recording the number of times the up and down switches are depressed.
A vehicle speed sensor 10 is arranged to input a speed indicative signal to a vehicle speed counter 12. A decoder 14 is connected with the counter 12 and arranged to convert the count data into a suitable control signal which is transferred to a speed data transmission circuit 16. As shown, the latter mentioned circuit is connected with a bus and arranged to transmit the speed indicative data to driver circuits 18, 20 included in the first and second display units. The driver circuits 18, 20 are respectively connected to a meter display unit 22 and a HUD display unit 24.
The illumination control circuit 8 is also operatively connected with the driver circuits 18 and 20 in a manner to selectively control the illumination for the same.
However, this arrangement has suffered from the drawbacks that the data which is bussed to the driver circuits 18 and 20 is apt to be influenced by noise such as high frequency radiation, short wave radio transmissions, static electricity and the like, such as tend to be generated by doppler radar systems, CB type radio communication systems and the like, and to cause the data which is displayed on the windshield and or instrument panel to undergo an undesirably deviation from that intended.
FIG. 13 shows a prior proposed vacuum fluorescent display (VFD) unit which has been utilized in the HUD and meter display units. This arrangement however has suffered from the drawbacks that appropriate illumination levels have not been adequately obtainable and therefore has hampered attempts to provide an arrangement which is both free of influence by external noise (and/or static electrical effects) and which therefore enables both accurate and clear images to be produced in the desired manner. A more detailed discussion of this arrangement will be made later in the instant disclosure in connection with a fifth embodiment of the invention.